The present invention relates to fluids useful for subterranean operations, and more particularly, to treatment fluids comprising surfactants and water soluble polymers, and methods of use employing such treatment fluids to treat low permeability shale formations.
Aqueous treatment fluids may be used in a variety of subterranean treatments. Such treatments include, but are not limited to, stimulation operations and completion operations. As used herein, the term “treatment,” or “treating,” refers to any subterranean operation that uses a fluid in conjunction with a desired function and/or for a desired purpose. The term “treatment,” or “treating,” does not imply any particular action by the fluid.
An example of a subterranean treatment utilizing an aqueous treatment fluid is hydraulic fracturing. The fractures may be created by introducing a fracturing fluid into the formation at a rate sufficient to exert a sufficient pressure on the formation to create and extend fractures therein. Solid fracture proppant materials, such as sand, may be suspended in the fracturing fluid so that upon introducing the fracturing fluid into the formation and creating and extending fractures therein, the proppant material may be carried into the fractures and deposited therein. Such a treatment may prevent the fractures from closing due to subterranean forces when the introduction of the fracturing fluid has ceased.
During the placement of aqueous treatment fluids into a well bore, a considerable amount of energy may be lost due to friction between the treatment fluid in turbulent flow and the formation and/or tubular goods (e.g., pipes, coiled tubing, etc.) disposed within the well bore. As a result of these energy losses, additional horsepower may be necessary to achieve the desired treatment. To reduce these energy losses, water soluble polymers have been included in aqueous treatment fluids as friction reducing polymers. The term “friction reducing polymer,” as used herein, refers to a polymer that reduces frictional losses due to friction between an aqueous fluid in turbulent flow and tubular goods (e.g. pipes, coiled tubing, etc.) and/or the formation.
Several conventional surfactants have also been used in treatment fluids in attempts to alleviate water and oil blocks within a formation. Surfactants, which contain a hydrophilic and a hydrophobic group, are mixed with a treatment fluid, inter alia, to lower the surface tension of the fluid in order to facilitate the cleanup and mitigate formation damage caused by either water blocks or gas condensates. In addition to lowering surface tension, surfactants also may change the formation wettability. This results from a decrease in the capillary pressure of the fluid in the flow channels in the subterranean formation, which may be accomplished by, among other things, changing the contact angle so that clean-up process can be very facile and hydrocarbon can flow with less resistance.
Cationic, anionic and zwitterionic surfactants may be used to enhance the production of hydrocarbons. While these surfactants have been used successfully, there may be disadvantages. In some instances, friction reducing polymers are incompatible with ionic surfactants used. The most common friction reducing polymers are anionic polymers based on acrylamide. It is believed that the ionic nature of such friction reducing polymers may cause these to interact with cationic or positively charged surfactants, and thereby form precipitates. The term “precipitate” as used herein, refers to a coagulated mass of particles in a liquid. The resulting precipitates may be undesirable because, among other things, the precipitates may facilitate the formation of agglomerates that may clog pumps, filters, surface equipment and possibly plug fractures. Similarly, precipitates may also reduce the fluid conductivity in the formation by adsorbing onto fracture faces within the formation impacts subsequent hydrocarbon production from the well bore. Moreover, the precipitated friction reducing polymer may lead to higher friction pressures resulting increased cost of fracturing. In addition, the precipitated surfactant may lower the capillary pressure of the fluid by not being able to properly adsorb to the rock surface, thus making the hydrocarbon recovery more difficult.